Coal is America's (and the world's) most abundant fossil fuel. The proven U.S. reserves of coal (in terms of energy content) are over 15 times greater than its reserves of oil and gas combined. This means that in excess of 80% of the U.S. fossil fuel supply (including oil shale) is in the form of coal. However, coal has three major drawbacks. (1) Coal is a solid and is less easily handled and transported than fluidic or gaseous materials. (2) Coal contains compounds which, on burning, produce the pollutants associated with acid rain. (3) Coal is not a uniform fuel product, varying in characteristics from region to region and from mine to mine.
In fossil fuels, the ratio of hydrogen atoms to carbon atoms is most important in determining the heating value per unit weight. The higher the hydrogen content, the more liquid (or gaseous) the fuel, and the greater its heat value. Natural gas, or methane, has a hydrogen-to-carbon ratio of 4 to 1 (this is the maximum); coal has a ratio of about 1 to 1; shale oil about 1.5 to 1; petroleum crude about 2.0 to 1; and gasoline almost 2.2 to 1.
Liquefaction of coal involves hydrogenation. If the coal has a hydrogen-to-carbon ratio of 1, and if the hydrogens on half the carbons could be transferred or "rearranged" to the other half of the carbons, then the result would be half the carbons with 0 hydrogens and half with 2 hydrogens. The first portion of carbons (with 0 hydrogens) is char; the second portion of carbons (with 2 hydrogens) is a liquid product similar to a petroleum fuel oil. If this could be accomplished using only hydrogen inherent in the coal, ie., no external hydrogen source, then the coal could be refined in the same economical manner as petroleum, yielding a slate of refined hydrocarbon products and char.